The Effect of Residence Time Distribution on the Slurry‐Phase Catalytic Ethylene Polymerization: An Experimental and Computational Study

This work is focused on the development and validation of a model accounting for the impact of the reactor residence time distribution in well‐stirred slurry‐phase catalytic polymerization of ethylene. Particle growth and morphology are described through the Multigrain model, adopting a two‐site model for the catalyst and a conventional kinetic scheme. Particle size distribution and polymer properties (average molecular weights and polydispersity) are computed as a function of particle size through a segregated model, assuming that neither breakage nor aggregation occur. Reactors are modeled by means of fundamental mass conservation equations. The model is applied to a system constituted by a series of two ideal continuous stirred tank reactors, where the synthesis of polyethylene with bimodal molecular weight distribution is performed, employing the initial catalyst size distribution as the only adjustable parameter. The model provides insights at the single particle scale for each specific size, thus highlighting the inhomogeneity which arises from the synergic effects of chemical kinetics and residence time distributions in both reactors. The satisfactory agreement between model results and experimental data, in terms of particle size distribution and average molecular weights, confirmed the suitability of the model and underlying assumptions.     

第一性原理研究MgZn2相的电子结构及磁性质

运用密度泛函理论的第一性原理计算分析了MgZn₂相的电子结构及相关磁性质。能带结构和态密度分析表明Zn4s和Zn4p轨道、Mg3s和Mg3p轨道分别发生sp态杂化,然后杂化态之间相互作用而形成Zn-Mg键;Mulliken布居分布计算显示:Zn₁-Mg(Zn₁是处于晶格边缘的Zn原子)和Zn₂-Mg(Zn₂是处于晶格内部的Zn原子)电子云重叠布居数接近0,电子密度分析显示Zn-Mg之间电子密度分布具有明显的定域性。结合上述结果与Zn、Mg原子的电负性差异,确定Zn-Mg键为极性共价键。分态密度(PDOS)分析显示,Zn₁-Mg键和Zn₂-Mg键的差异主要表现在Zn₂4s轨道在-10~-6 eV区域对成键的贡献度高于Zn₁4s轨道,而Zn₁4s轨道在2~5 eV区域对成键的贡献度高于Zn₂4s轨道。进一步对MgZn₂的积分自旋态密度和磁矩计算表明:MgZn₂磁性质表现为顺磁性,其磁性主要来源于Zn₁-Mg键中的2个自旋相同的未配对电子;MgZn₂的顺磁性特性将使Al-Zn-Mg-Cu(7xxx系)高强铝合金产生磁致塑性效应。     

A theoretical investigation into the conformational changes of dibenzo-p-dioxin, thianthrene, and selenanthrene

Theoretical ab initio calculations using the HF and B3LYP methods have been carried out to investigate the conformational differences of three cyclic rings, dibenzo-p-dioxin (DPD), thianthrene (THT), and selenanthrene (SET). The physical origin for the conformational preference of each molecule has been studied using the natural bond orbital (NBO) analysis. The NBO results indicate that DPD exists in a planar form due to strong electron delocalization caused by the specific orbital interaction, around the X atom. On the other hand, THT and SET exist as puckered forms with high inversion barriers due to less effective electron delocalization. The NBO analysis also shows that the conformational stabilization in DPD is caused by a more effective overlap of the orbitals, compared with the overlap of the orbitals in THT.     

Theoretical study of 3d‐metal mononitrides using DFT method

3d‐Metal mononitrides are studied using the density functional theory method. The lowest spin state for these dimers is obtained using the B3LYP hybrid functional with the 6‐311+G* basis set. The equilibrium geometries, vibrational frequencies, binding energies, Mulliken, and natural orbital population analysis charges, natural orbital electronic configuration, electron affinity, and ionization potential are obtained. Mulliken as well as natural orbital population analysis charges indicate that for all dimers, in cations most of the positive charge localized on the transition metal atom where in anions most of the negative charge localized on nitrogen atom. The binding energies for 3d‐metal mononitrides are higher than those for monocarbides and monoxides. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Quantitative ultra‐high‐performance liquid chromatography–tandem mass spectrometry for determination of dexmedetomidine in pediatric plasma samples: Correlation with genetic polymorphisms

Dexmedetomidine is an important sedative agent administered as premedication to achieve procedural sedation in children. To describe the correlation between the genetic state and the concentration of dexmedetomidine, it is necessary to develop a specific, time‐saving and economical method for detection of dexmedetomidine in plasma samples. In this work, an ultra‐high‐performance liquid chromatography (UHPLC)–tandem mass spectrometry method has been established and validated for detection of dexmedetomidine in plasma from pediatric population. After a simple liquid–liquid extraction with an organic solution, the analytes were separated on an ACQUITY BEH C₁₈ column (2.1 mm × 50 mm, 1.7 μm particle size) by gradient elution with the mobile phase of acetonitrile and 1‰ aqueous formic acid (flow rate 0.3 mL min^?1). Mass spectrometry measurements were performed under the positive selected reaction monitoring and the mass transitions monitored were m/z 201.3 → 95.1, 204.2 → 98.0 for dexmedetomidine and deuterated medetomidine (internal standard), respectively. Validation of the method based on China Food and Drug Administration guidelines showed acceptable selectivity. The UHPLC method employed a stable isotope‐labeled internal standard, showed good specificity and was successfully used to detect dexmedetomidine in plasma samples from 260 pediatric patients. A subsequent application of this method to a pharmacogenetic study was also described. Importantly, this is the first study to report the correlation between CYP2A6 rs835309 activity and concentration of dexmedetomidine.     

Analysis of B3LYP and MP2 conformational population distributions in trans‐nicotine,acetylcholine, and ABT‐594

This work presents an analysis of the equivalence of MP2 and DFT (B3LYP functional) conformational populations. As a test case, we select three cholinergic agents (trans‐nicotine, acetylcholine, and the nicotinic analgesic ABT‐594), where the minima on the conformational energy hypersurfaces expand a large range of energies (～0–30 kJ mol^?1). From energetic and structural data obtained in vacuo at the MP2 and B3LYP/cc‐pVDZ levels, we build conformational partition functions, including the effect of the conformational kinetic energy and the rotovibrational coupling. Our results at a physiological temperature (37°C) show qualitative agreement in all cases. Quantitative agreement, however, is only found for trans‐nicotine and ABT‐594. In the first case, energy minima differ by <0.2 kJ mol^?1. Therefore, the equivalence of structural results translates in the equivalence of the conformational distribution. For ABT‐594, the minima are separated by as much as 8.0 kJ mol^?1, and the conformational energy determines the conformational distribution. In this case, the slight relative variation of conformational energy, between B3LYP and MP2, does not affect the population, since the secondary minima are high in energy and very low in population. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Estimating reaction parameters in mechanism-enabled population balance models of nanoparticle size distributions: A Bayesian inverse problem approach

In order to quantitatively predict nano- as well as other particle-size distributions, one needs to have both a mathematical model and estimates of the parameters that appear in these models. Here, we show how one can use Bayesian inversion to obtain statistical estimates for the parameters that appear in recently derived mechanism-enabled population balance models (ME-PBM) of nanoparticle growth. The Bayesian approach addresses the question of “how well do we know our parameters, along with their uncertainties?.” The results reveal that Bayesian inversion statistical analysis on an example, prototype nanoparticle formation system allows one to estimate not just the most likely rate constants and other parameter values, but also their SDs, confidence intervals, and other statistical information. Moreover, knowing the reliability of the mechanistic model's parameters in turn helps inform one about the reliability of the proposed mechanism, as well as the reliability of its predictions. The paper can also be seen as a tutorial with the additional goal of achieving a “Gold Standard” Bayesian inversion ME-PBM benchmark that others can use as a control to check their own use of this methodology for other systems of interest throughout nature. Overall, the results provide strong support for the hypothesis that there is substantial value in using a Bayesian inversion methodology for parameter estimation in particle formation systems.     

去甲万古霉素群体药代动力学与药效学优化研究

目的研究去甲万古霉素群体药代动力学指标差异,对患者进行药效学优化。方法选取2015年1月至2015年12月268例感染患者,将其按照年龄分为中青年组和老年组,每组各134例,采用群体药代动力学和药效学优化公式进行计算,分析患者上述指标差异。结果青年组与老年组的群体药代动力学各项指标差异明显具有统计学意义(P0.05)。结论感染患者通过去甲万古霉素药物治疗疗效确切,对革兰阳性菌的杀灭作用明显,采用群体药代动力学和药效学研究后发现,AUC24/MIC能够作为去甲万古霉素的应用指标,并以此指导临床用药效果显著,值得临床应用推广。